ELASTIC THICKNESS OF THE LITHOSPHERE IN THE MARQUESAS AND SOCIETY ISLANDS

Analysis of sea surface gravity data along six profiles collected duri ng the Crossgrain 2 and EW9103 expeditions to the Marquesas Islands de monstrates that the elastic plate thickness T(e) is remarkably uniform , with a value of 18+/-2 km over the entire chain. Given the 50 Ma age of the Marquesan lithosphere at the time of loading, this T(e) value agrees with the empirical relationship between elastic plate thickness and plate age for hotspot volcanoes in the North Pacific, Atlantic, a nd Indian oceans. Using more limited gravity data from the Society cha in, we find that the best fitting elastic plate thickness there is res olvably higher, 23+/-2 km. In both cases, our values for T(e) are larg er than those derived from analysis of satellite altimetry profiles. W e attribute the low T(e) values derived from satellite altimetry to in accuracies in available gridded bathymetric databases for this pan of the world and the assumption of a high value for the density of the se afloor. Although our shipboard data sample only two French Polynesian island chains, the results suggest that the amount of elastic plate th inning over the South Pacific Superswell may be less than previously p roposed, thus eliminating conflict between estimates of the thermal st ructure of the Superswell lithosphere as derived from elastic plate th ickness and that derived from heat flow, depth anomalies, and love wav e dispersion.